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Worst/most costly mistake?

Just curious, what has been the worst or most costly mistake you've ever made on the job?

My dad once told me a story that a buddy of his was working on a furnace at a trailer house, and after he left he got a call on the radio that the trailer had burned down as soon as he left due to a gas leak igniting...

I'm an apprentice, and a couple months ago I was replacing a compressor for a walk in cooler (by myself) and I had forgotten to take out the rubber plug inside the suction stub on the compressor. We got a no cool call a couple weeks later on that walk in, come to find out it obviously ruined the compressor. It was about a thousand dollar compressor- luckily it was covered under warranty lol. I'm surprised it lasted that long!

Oh boy did i learn from it haha.. never made that mistake again. For some reason it looked fine on start up, but when we condemned the compressor and saw the plug still in the suction stub it was pretty torn up.

In recent memory, I almost caused the complete destruction of a 60 ton Trane Recip. compressor.
I was assisting one of our other less "experienced" techs doing some leak repairs on the compressor. ( I was supposed to be there for technical support, and really messed this one up) One of the leak areas was around the bearing cover. In order to repair the leak, the oil pump had to be removed from the compressor. I removed it as one piece and stacked the pieces on a rag nearby so I could put it back in place the same way it came out. Needless to say, While working, I accidentally hit the pieces of the pump and knocked them over. So, rather than go to my truck and search for the compressor repair literature, I decided that I remember how it came out. I put it back in place the way I "thought" it came out. we completed the repair and did the leak check / evacuation on the circuit. We charged the 120 lbs of refrigerant back into the circuit. Due to me not being sure that the oil pump was in the correct way, I decided to monitor the oil pressure to make sure the oil pump was pumping. Well.... when we started it up, guess what.... no oil pressure. So now we have a problem. I have to re order the gaskets to rebuild the oil pump covers. We leave the compressor off until the gaskets arrive. I went in on a weekend to do the repairs since the customer shouldn't have to pay for my mistake. I went in on Saturday morning and isolated the compressor. I evacuated the remaining refrigerant and started preparation to do the work. Well. undoubtedly the liquid line service valve leaked by because by the time i had my stuff set up to remove the oil pump cover, the compressor built up pressure to about 5 PSI. I didn't notice it until I started taking bolts out of the oil cover. When I got the last bolt removed, I tapped the oil cover with a hammer. Much to my surprise, the oil pump cover sprang out and oil started spraying everywhere. Before I could get the cover back in place the entire 2 gallon oil charge had sprayed out all over the chiller, me, the wall and the ground.... As an aside, I also now know that it takes almost 75 lbs of oil dry and a half a box of rags to dry up 2 gallons of oil.
Furthermore, in the short 30 seconds of time that the compressor ran without oil, the oil pump was damaged as well as the thrust bearing. Luckily we had those parts on site still new from a previous repair to a compressor that the customer decided to replace instead of repair.
After recovering the refrigerant I had initially pumped into the condenser, I installed the bearing and oil pump like it should be, put the compressor back together, and evacuated the circuit. I then recharged the circuit and restarted the compressor. This time, we had oil pressure, and the compressor ran like it was supposed to.
Lesson Learned. Next time, I will definitely take the time to make sure the oil pump is back in correctly.

I have two circumstances in the first year I started service. First one, I was checking a cap on an indoor blower and the breaker to the elec furnace was labled wrong. So, instead of checking with my meter to confirm (which you're always supposed to do) I shorted the cap to the blower housing with my needle nose and fried the board, X-frmer, and heat anticipator! Another instance There was a faded jug of r-134a that looked like r-22 and I forced it into a system. Had to recover, pull vacuum, add drier, and recharge system. Yep, made my fare share of mistakes!

Once upon a time many moons ago, as a Jr. engineer, I specified the wrong motors for a big ole' ob for one of them big ole' manufacturers. We put in 1/2 HP PSC's at the factory and they were supposed to be 3/4 HP. The systems were unit ventilators with a combination of steam, hot water and chilled water coils. The units were shipped and installed in the Milwaukee ISD and there were, oh, about 750 of them. Well, guess who gets to go to Milwaukee and change out 750 motors? I didn't personally do much of the work but I had to hire local union guys and deal with the pissed off principal and administrators. I had to train the union guys on how to change the motors and supply them with the specialty tools needed. They were the same ones who did the initial install. The time frame for the work? Between 4:00 pm and 6:00 am when the classrooms were empty. I swear one of the high schools was the freakin size of the Mall of the Americas. I was given the alarm codes and a set of master keys which made life tolerable. Ever walk up and down the halls of a gigantic school at 3 am when half the time you can't find the lights? After 2 weeks of this I started lose track of which ones were fixed and which ones weren't. And I never but never let those union guys know I was the schmuck who hosed the job. I got it done though and returned home a hero in my own mind.

It wasn't totally my fault though, there were other breakdowns in QC and engineering but man I took a ribbing for it. The total cost was somewhere around 100K. A few months later I got a promotion and a nice raise.

The picture in my avatar is of the Houston Ship Channel and was taken from my backyard. I like to sit outside and slap mosquitos while watching countless supertankers, barges and cargo ships of every shape and size carry all sorts of deadly toxins to and fro. It's really beautiful at times.....just don't eat the three eyed fish....

When I was fairly new to the trade, I condemned a 7.5 ton 3 phase compressor. When trying to start, it would make a loud humming noise and draw locked rotor amps. Well, I checked supply voltage and it was good. (first mistake, didn't check load voltage) I amped one of the legs instead of all three (2nd mistake) and ordered new compressor (3rd mistake). Recovered refer, removed compressor and installed new comp. and filter/drier, evacuated, recharged and hit the power. Same thing happened. Turns out, one of those Japanese/Asian beetle ladybugs was wedged between the load side contacts on L3. Removed bug. Unit was fine. This was warranty, so the customer did not pay anything. I'm sure Copeland wondered why that comp. was sent back though.

A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
Gene Castagnetti-Director of the National Memorial Cemetery of the Pacific in Hawaii

I was installing a new pannel in a house, about 10 years ago. It was an outdoor pannel I was replaceing, the main pannel was on the other side of the wall I was working on. I was in the process of finising running my circuits on the new pannel and the home owner was bugging the hell out of me to get the power on so she could dry clothes.

The service was an old two wire with ground. No neutral was ran so the ground was also used as the grounded conductor, witch was normal on old installations. I had the lines tied into the pannel but had inadvertantly missed the ground connection before I restored power so she could dry her clothes.

When I restored power all the 120 volt circuits came online as well as the dryer. Now we had a large unbalanced load with no grounded conducter to carry the unbalanced load back it's sorce. So it brought all the 120 volt circuits up to 220, and fried all the electronics in the house. About $7,000 worth of damage, insurance replaced everything and I got all the electronics that got fried and was able to repair about 90% of everthing so it all turned out good in the end. I've still go the TV, computer, and microwave oven.

In my early days, I toasted a single phase compressor by simply connecting the power wrong. In a more recent, embarrassing (confession is good for the soul!) episode, ran into a toasted compressor in a new package unit year before. It had open windings, I'd checked all legs, yep, got a new compressor from mfr, put it in. It ran ok at check out, but then a week or so later, called back and it was toasted AGAIN. So, I did what I should've done to begin with started checking EVERYTHING, found the installing electricians had jammed one of the line power wires all the way up between the contactor points! DROPPED a brand new blower motor while roping it up, on a Friday, at a brand new school, with school starting on Monday, and it had been shipped in . . . had to do 70 mile RT to a local motor shop, get a SUBSTITUTE motor, go back and modify the mount to get cooling going.

G T T

“In the end we will remember not the words of our enemies, but the silence of our friends”

Years ago fresh out of school, while changing and oil filter on a tank. The little top air bleeder screw came flying out while bleeding air out of it. I could not find it and panicked, went to van to look for new filter and by the time I got back oil was everywhere.. I was too dumb and green to turn off tank valve.. what a mess, called the boss and got into lots of trouble. lesson learned. Couple of small mess ups here and there over the years. Learned from each of them..